LastPass wrote about the vulnerability on Wednesday and said that a fix is already out for Firefox users.

Google security research Tavis Ormandy first discovered the issue. When examining the password manager, he tweeted on Tuesday, "Are people really using this lastpass thing? I took a quick look and can see a bunch of obvious critical problems. I'll send a report asap."

Any vulnerability with LastPass could pose a big risk for users. The popular software is supposed to securely store and autofill all the passwords users have for their different sites.

Ormandy isn't the only security researcher to find flaws with the password manager. On Wednesday, Mathias Karlsson at Detectify Labs said that he had also managed to hack LastPass -- in this case, to steal user passwords.

He did so by exploiting a bug in the password manager's Chrome browser extension, Karlsson wrote in a blog post.

Typically, the LastPass browser extension autofills the password to certain websites the user visits. However, Karlsson noticed that the extension added some HTML code to every site it visits. This code is meant to parse the website's address to identify the domain and then fill in the required password.

The problem is that the HTML code can be tricked. The extension will autofill a user's password, even when it isn’t visiting the correct website.

Karlsson exploited the bug, and created a fake URL, fooling the LastPass browser extension into thinking it was visiting Twitter. The extension then autofilled the Twitter password into the site.

A hacker could take advantage of this flaw, by building a malicious website and tricking LastPass users into visiting it. The website could then secretly collect the passwords.

Karlsson reported the bug over a year ago, and the problem has since been fixed, according to LastPass. It noted that both vulnerabilities would require the hacker tricking the user into visiting a malicious site for them to work.

The company is advising users to be on the watch for phishing attacks that can send links to unsavory websites.